1. Field Of The Invention
The present invention relates to signal sampling circuits. More specifically, the present invention is directed to a signal sampling circuit having signal isolating means for conductively isolating a signal input circuit from a signal output circuit.
2. Description Of The Prior Art
A prior art sampling circuit with a signal isolating capability used a first transformer to couple a signal input circuit to a signal output circuit. Switches were provided on the primary and secondary sides of the transformer and were synchronously operated to sample an input signal. A second transformer is used to couple a switch energizing signal to the sampling switches on the primary and secondary sides of the first transformer. Such a prior art circuit requires shielding between the transformers and is uneconomical because of the added cost of a second transformer. Another prior art circuit used a photocoupler to directly transfer an input signal from an input circuit to an output circuit. This prior art circuit required a conversion of the input signal to a pulse-width modulated signal before transmission by the photocoupler, and a demodulation after transmission by the photocoupler. Thus, this prior art circuit is more complicated than the aforesaid prior art circuit and even less economical as a result of the expensive converter circuits and their isolated power supplies.